The DRM_BUS_FLAG_PIXDATA_(POS|NEG)EDGE and
DRM_BUS_FLAG_SYNC_(POS|NEG)EDGE flags are deprecated in favour of the
new DRM_BUS_FLAG_PIXDATA_(DRIVE|SAMPLE)_(POS|NEG)EDGE and
new DRM_BUS_FLAG_SYNC_(DRIVE|SAMPLE)_(POS|NEG)EDGE flags. Replace them
through the code.

This effectively changes the value of the .sampling_edge bridge timings
field in the dumb-vga-dac driver. This is safe to do as no driver
consumes these values yet.
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Reviewed-by: NStefan Agner <stefan@agner.ch>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omap_dss_device type and output_type fields differ mostly for
historical reasons. The output_type field is required for all devices
but the display at the end of the pipeline, and must be set to
OMAP_DISPLAY_TYPE_NONE for the latter. The type field is required for
all devices but the internal encoder, for which it is ignored.

The only reason why the output_type field must be set to
OMAP_DISPLAY_TYPE_NONE for the display at the end of the pipeline is to
identify omap_dss_device instances corresponding to displays. This is
not documented and confusing.

Clean the code by adding a new display field to the omap_dss_device
structure to identify displays, and merge the type and output_type
fields.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omap_dss_device .check_timings() and .set_timings() operations
operate on struct videomode, while the DRM API operates on struct
drm_display_mode. This forces conversion from to videomode in the
callers. While that's not a problem per se, it creates a difference with
the drm_bridge API.

Replace the videomode parameter to the .check_timings() and
.set_timings() operations with a drm_display_mode. This pushed the
conversion to videomode down to the DSS devices in some cases. If needed
they will be converted to operate on drm_display_mode natively.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The source pointer will be removed to the omap_dss_device structure.
Store it internally in the DSI panel driver data.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Instead of manually iterating over the dss devices in the pipeline to
find the first one that implements the .get_modes() operation, add a new
operation flag for .get_modes() and use the omap_connector_find_device()
helper function to locate the right dss device.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Now that the .get_modes() operations takes a drm_connector and fills it
with modes, it becomes easy to fill display information in the same
operation without requiring a separate .get_size() opearation.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

omap_dss_device operations expose fixed video timings through a
.get_timings() operation that return a single timing for the device. To
prepare for the move to drm_bridge, modify the API to instead add DRM
modes directly to the connector.

As this puts more burden on display devices, we also create a helper
function for panels to add a single DRM mode from the panel video
timings.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omapdrm and omapdss drivers are architectured based on display
pipelines made of multiple components handled from sink (display) to
source (DSS output). This is incompatible with the DRM bridge and panel
APIs that handle components from source to sink.

Reconcile the omapdrm and omapdss drivers with the DRM bridge and panel
model by reversing the direction of the DSS device .enable() and
.disable() operations. This completes the move to the DRM bridge model,
with the notable exception of the DSI pipelines that will require more
work.

We also adapt the omapdss shutdown handler dss_shutdown() to shut down
all active pipelines starting from the pipeline output device instead of
the display device.

As a consequence the for_each_dss_display() macro isn't used and can be
removed, and the omapdss_device_get_next() function underlying the macro
can be simplified to search for output devices only.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The displays (connectors, panels and encoders) bail out from their
.enable() and .disable() handlers if the dss device is already enabled
or disabled. Those safety checks are not needed when the functions are
called through the omapdss_device_ops, as the .enable() and .disable()
handlers are called from the DRM atomic helpers that already guarantee
that no double enabling or disabling can occur.

However, the handlers are also called directly from the .remove()
handler. While this shouldn't be needed either as the modules can't be
removed as long as the device is in use, it's still a good practice to
disable the device explicitly. There is currently a safety check in
.remove() in some drivers but not all of them.

Remove the safety checks from the .enable() and .disable() handlers, and
add missing ones in the .remove() handler.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The displays (connectors, panels and encoders) return an error from
their .enable() handler when the dss device is not connected. They also
disconnect the dss device explicitly from their .remove() handler if it
is still connected.

Those safety checks are not needed:

- The .enable() handler is called from code paths that access the dss
  devices chain from the display device, which is set to NULL when the
  device isn't connected.

- The .remove() handler can only be called when unloading the module as
  the driver has the suppress_bind_attrs attribute set, and a reference
  to the module is taken when constructing the dss devices chain, so the
  module can only be unloaded when the dss device is disconnected.

Remove the safety checks.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

All .enable() and .disable() handlers for panels and connectors share
common code that validates and updates the device's state. Move it to
common locations in the omap_encoder_enable() and omap_encoder_disable()
handlers.

The enabled check in the .disable() handler is left untouched, it will
be addressed separately.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Tested-by: NSebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

panel-dpi used to convey the bus-flags via the videomode, but recent
changes changed the use of videomode to DRM's drm_display_mode which
does not contain bus-flags. This broke panel-dpi, which didn't
explicitly store the bus-flags into dssdev->bus_flags.

Fix this by setting dssdev->bus_flags. Also change the bus_flags type to
u32, as that is the type used in the DRM framework, and we would get a
warning with drm_bus_flags_from_videomode() otherwise.

Fixes: 3fbda31e ("drm/omap: Split mode fixup and mode set from encoder enable")
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>
Reported-by: NH. Nikolaus Schaller <hns@goldelico.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181126092447.11864-1-tomi.valkeinen@ti.comReviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>

Instead of calling the .set_timings() operation recursively from the
display device backwards, iterate over the devices manually in the DRM
encoder code. This moves the complexity to a single central location and
simplifies the logic in omap_dss_device drivers.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Panels drivers store their timings in a device data structure field that
is initialized at probe time, either from hardcoded values or from
firmware-supplied values. Those timings are then reported through the
.get_timings() operation to construct the panel display mode.

The panel timings are further modified by the .set_timings() operation,
which is called with the timings retrieved by .get_timings(), and
mangled by .check_timings(). The latter potentially adjusts the pixel
clock only.

Conceptually, modifying the panel timings is wrong, as the timings are
an intrinsic property of the panel and should thus be fixed.
Furthermore, modifying them this way at runtime can result in display
modes reported to userspace varying between calls, which is also wrong.

There's no actual need to store the mangled pixel clock value in the
timings. Don't modify the panel timings in the .set_timings() operation,
just forward it to the previous device in the display pipeline.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The analog TV, DVI and HDMI connectors all report timing information
through the .get_timings() information.

For analog TV outputs the information is queried from the encoder, so
the operation is unused. Remove it.

For HDMI outputs the display pipeline provides EDID capability, so the
operation is unused as well. Remove it.

For DVI outputs the operation is also unused if the pipeline provides
EDID capability. Otherwise (when the DDC bus is not connected) we
shouldn't hardcode a single mode, but instead report no mode and let the
KMS core add default modes. This is achieved by removing the operation.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The .check_timings() operation is called recursively from the display
device back to the output device. Most components just forward the
operation to the previous component in the chain, resulting in lots of
duplicated pass-through functions. To avoid that, iterate over the
components manually.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Source components in the display pipeline need to configure their output
signals polarities and clock driving edge based on the requirements of
the sink component.

Those requirements are currently shared across the whole pipeline in the
flags of a videomode structure, instead of being local to each bus. This
both prevents multiple buses from having different configurations (when
the hardware supports it), and makes it difficult to move from videomode
to drm_display_mode as the latter doesn't contain bus polarities and
clock edge flags.

Add a bus_flags field to the omap_dss_device structure and move the
DISPLAY_FLAGS_DE_(LOW|HIGH), DISPLAY_FLAGS_PIXDATA_(POS|NEG)EDGE and
DISPLAY_FLAGS_SYNC_(POS|NEG)EDGE videomode flags to bus_flags in all
external encoders, connectors and panels. The videomode flags are still
used internally for internal encoders, this will be addressed in a
second step.

The related videomode flags in the default mode of the DVI connector can
simply be dropped, as they are always overridden by the TFP410 driver.
Note that this results in both the DISPLAY_FLAGS_SYNC_POSEDGE and
DISPLAY_FLAGS_SYNC_NEGEDGE flags being set, which is invalid, but only
the former is tested for when programming the DISPC, so the DVI
connector flags are effectively overridden by the TFP410 flags.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omap_dss_device .set_timings() operation for external encoders
stores the video mode in the device data structure. That mode is then
never used again. Drop it.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omap_dss_device .set_timings() operations are called directly from
omap_encoder_update(), and indirectly from the omap_dss_device .enable()
operation. The latter is called from omap_encoder_enable(), right after
calling omap_encoder_update(). The .set_timings() operation it thus
called twice in a row. Fix it by removing the indirect call.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The .set_timings() operations of the omap_dss_device instances don't
need to modify the passed timings. Make the pointer const.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Both the .check_timings() and .set_timings() handlers call
tfp410_fix_timings() to fix the timing's flags. As .check_timings() is
always called before .set_timings(), there's no need to fix the flags
twice. Remove the tfp410_fix_timings() call from .set_timings().
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The HDMI mode (.set_hdmi_mode()) and infoframe (.set_infoframe())
operations are called recursively from the display device back to the
HDMI encoder. This isn't required, as all components other than the HDMI
encoder just forward the operation to the previous component in the
chain. Call the operations directly on the HDMI encoder.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Instead of calling the EDID read operation (.read_edid()) recursively
from the display device back to the first device that provides EDID read
support, iterate over the devices manually in the DRM connector code.
This moves the complexity to a single central location and simplifies
the logic in omap_dss_device drivers.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

On HDMI outputs, CEC support requires notification of HPD signal
deassertion. The HPD signal can be handled by various omap_dss_device
instances in the pipeline, and all of them forward HPD events to the
OMAP4 internal HDMI encoder.

Knowledge of the DSS internals need to be removed from the
omap_dss_device instances in order to migrate to drm_bridge. To do so,
move HPD handling for CEC to the omap_connector.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omap_dss_device .enable_hpd() and .disable_hpd() are used to enable
and disable hot-plug detection at omapdrm probe and remove time. This is
required to avoid reporting hot-plug detection events before the DRM
infrastructure is ready to accept them, as that could result in crashes
or other malfunction.

Hot-plug event reporting is conditioned by both HPD being enabled
through the .enable_hpd() operation and by the HPD callback being
registered though the .register_hpd_cb() operation. We thus don't need a
separate enable operation if we can guarantee that callbacks won't be
registered too early.

HPD callbacks are registered at connector initialization time, which is
too early to start reporting HPD events. There's however nothing
blocking a move of callback registration to a later time when the
omapdrm driver calls the HPD enable operations. Do so, and remove the
HPD enable operation completely from omap_dss_device drivers.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The HPD-related omap_dss_device operations are now only called when the
device supports HPD. There's no need to duplicate that check in the
omap_dss_device drivers. The .register_hpd_cb() operation can as a
result be turned into a void operation.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Instead of calling the hot-plug detection callback registration
operations (.register_hpd_cb() and .unregister_hpd_cb()) recursively
from the display device back to the first device that provides hot plug
detection support, iterate over the devices manually in the DRM
connector code. This moves the complexity to a single central location
and simplifies the logic in omap_dss_device drivers.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Instead of calling the .detect() operation recursively from the display
device back to the first device that provides hot plug detection
support, iterate over the devices manually in the DRM connector
.detect() implementation. This moves the complexity to a single central
location and simplifies the logic in omap_dss_device drivers.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

omap_dss_device instances have two ops structures, omap_dss_driver and
omap_dss_device_ops. The former is used for devices at the end of the
pipeline (a.k.a. display devices), and the latter for intermediate
devices.

Having two sets of operations isn't convenient as code that iterates
over omap_dss_device instances need to take them both into account.
There's currently a reasonably small amount of such code, but more will
be introduced to move the driver away from recursive operations. To
simplify current and future code, move all operations that are not
specific to the display device to the omap_dss_device_ops.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The GPIO descriptor API is favoured over the plain GPIO API for consumer
drivers. Using it simplifies the driver code.

As the descriptor API handles the active-low flag internally we need to
invert the polarity of all GPIO operations in the driver. Rename the
nreset_gpio field to reset_gpio to reflect that.

The reset GPIO is mandatory, so drop conditional tests through the
driver.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The driver doesn't use GPIOs and thus doesn't need to include the
linux/gpio.h header.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The GPIO descriptor API is favoured over the plain GPIO API for consumer
drivers. Using it simplifies the driver code.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The GPIO descriptor API is favoured over the plain GPIO API for consumer
drivers. Using it simplifies the driver code.

The reset GPIO is mandatory, so drop conditional tests through the
driver. The qvga GPIO is unused, so drop it completely.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The GPIO descriptor API is favoured over the plain GPIO API for consumer
drivers. Using it simplifies the driver code.

As the descriptor API handles the active-low flag internally we need to
invert the polarity of all GPIO operations in the driver.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The GPIO descriptor API is favoured over the plain GPIO API for consumer
drivers. Using it simplifies the driver code.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The .get_mirror() and .set_mirror() omap_dss_driver operations are
implemented by the panel-tpo-td043mtea1 driver but are never used.
Remove them.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omapdrm and omapdss drivers are architectured based on display
pipelines made of multiple components handled from sink (display) to
source (DSS output). This is incompatible with the DRM bridge and panel
APIs that handle components from source to sink.

To reconcile the omapdrm and omapdss drivers with the DRM bridge and
panel model, we need to reverse the direction of the DSS device
operations. Start with the connect and disconnect operations.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Look up the next dssdev at probe time based on device tree links for all
DSS outputs and encoders. This will be used to reverse the order of the
dssdev connect and disconnect call chains.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The connect handle of the analog TV and HDMI connectors casts the dssdev
to panel data only to then access fields of the panel data that are also
present in the dssdev. Remove the cast and use dssdev directly.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

The omapdss_of_find_source_for_first_ep() function locates the source
corresponding to the first endpoint of the first port of a device node.
We can easily extend it to locate sinks as well by passing the port
number as a parameter. This will be useful to find sinks in encoders
drivers.

Extend the function and rename it to omapdss_of_find_connected_device()
to reflect its new extended purpose.

Additionally, it is useful to differentiate between failures to return
the connected device because no link exists in the device tree for the
requested port, or because the connected device as described in the
device tree is invalid or not probed yet. Return NULL in the first case
and an error code in the second case, and update the callers
accordingly.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: NSebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>